1. Field of the Disclosure
The present disclosure relates to a passive keyless system, and more particular, a passive keyless system capable of suppressing power consumption of a portable device.
2. Description of the Related Art
In recent years, a passive keyless system is put to practical use which performs vehicle operations such as locking or unlocking of a door of a vehicle or start-up of an engine (hereinafter, abbreviated as vehicle operations) without using a mechanical key. In the passive keyless system, if a user is in possession of, for example, a portable device in a pocket of clothing or in a bag, the user is able to perform the vehicle operations described above without taking out and operating the mechanical key. As an example of such a system, a passive keyless system disclosed in Japanese Unexamined Patent Application Publication No. 2006-225975 is proposed.
FIG. 10 shows a passive keyless system of the related art according to Japanese Unexamined Patent Application Publication No. 2006-225975. As shown in FIG. 10, the passive keyless system of the related art includes a portable unit 201 (portable device), a mechanical key 202 that is detachably attached to the portable unit 201, and an in-vehicle system 203 mounted on a vehicle. The in-vehicle system 203 includes an in-vehicle control unit 230, in-vehicle transmitting means 231 and in-vehicle receiving means 232. The in-vehicle transmitting means 231 wirelessly sends a request signal to the portable unit 201. The portable unit 201 is activated by a battery. As the battery, for example, a button type battery is used. Then, the portable unit 201 wirelessly sends an ID signal in response to the request signal from the in-vehicle transmitting means 231. The in-vehicle receiving means 232 receives an ID signal from the portable unit 201. When an authentication of the ID signal received from the in-vehicle receiving means 232 is established, the in-vehicle control unit 230 allows vehicle operations using the portable unit 201. The mechanical key 202 is used as an emergency key.
Generally, in the passive keyless system, since battery replacement of a portable device is costly and takes effort, it is desirable that a period during which the portable device is usable without battery replacement, that is, a period, from when a new battery is installed in a portable device up to when the battery remaining amount becomes drained and the portable device becomes unusable, be at least a long time period.
However, in the passive keyless system of the related art according to Japanese Unexamined Patent Application Publication No. 2006-225975, the portable unit 201 (portable device) always waits for a request signal from the in-vehicle transmitting means 231 regardless of the remaining amount value of the battery. Therefore, the portable unit 201 always is needed to activate a circuit for reception, and power consumption of the portable unit 201 is large. If the power consumption of the portable unit 201 is large, the reduction in the remaining amount of the battery is accelerated. Since this become a factor to shorten a usable period of the portable unit 201, it is necessary to suppress the power consumption of the portable unit 201.